1. Field of the Invention
This invention relates to a moving subject recognition device for an automotive vehicle which is incorporated with an anticollision system.
2. Description of Related Art
In recent years, what is called an advanced safety vehicle provided with an anticollision system has been proposed. Some types of anticollision systems employ a combination of radar forward looking sensor and a brake. Such an anticollision system is known from, for example, Japanese Unexamined Patent Publication No.5-54297.
Typically, anticollision systems or collision avoiding systems detect moving vehicles, stationary subjects such as roadway structures ahead in the traveling path of the vehicle and provide an warning or automatically apply brakes when detects that there is a danger of causing a collision between the vehicle and subjects.
It has been obtained from many statistic analysis of traffic accidents or collisions that persons, who were involved in fatal car accidents are on foot, in particular during crossing a roadway, in many cases. Accordingly, avoiding involvement in a collision against a pedestrian crossing the roadway by use of such an anticollision system is contributory to a significant reduction in the fatality rate of a vehicle. The conventional anticollision system can recognize a pedestrian in the roadway as a moving subject which is in the danger of being hit by the vehicle and try to avoid a collision against the pedestrian. Since, as watched from the vehicle, it can be said that a pedestrian who is going to across a traveling path ahead the vehicle rushes out into the roadway, it is thought that there are many cases where, even if the anticollision system detects the pedestrian as a subject in danger of being possibly hit by the vehicle immediately after he or she rushes out into the roadway, it is already too late for the anticollision system to avoid a collision.
On a foot passenger who is presently out of a traveling path ahead the vehicle and, however, is possibly expected to cross the traveling path before long, it is necessary for the vehicle to recognize the passenger as a subject in danger of being hit by the vehicle even before the passenger appears into a traveling path ahead the vehicle. Most of pedestrians reflect radar beams less than vehicles and roadway structures. When increasing the response sensitivity of the radar in order to detect such a pedestrian, it is hard for the radar to extract beams reflected by the pedestrian only due to an increased disturbance caused by the surroundings. In particular, roadway structures, such as guardrail or crash barriers show reflection patterns similar to those of persons on foot and, accordingly, are hardly distinguishable from those persons. In other words, guardrails arranged at appropriate separations along the roadway are recognized just like fragmentary bodies in subject recognizing process as watched from the vehicle. Especially, when the guardrails are at close distances to the vehicle, there is considerable chance of grasping the guardrails like moving subjects having apparent lateral velocities including a lower recognition target threshold of 0.6 m/sec. for pedestrians due to the measuring accuracy of a laser radar.
If the anticollision system always reacts on every pedestrian out of the roadway, it is caused too frequently to travel. For this reason, the anticollision is needed to react only on pedestrians who cross the roadway ahead of the vehicle and are possibly expected to be involved in a collision. As a result, there is a strong demand for an algorithm for precise detection of pedestrians who are crossing the roadway exposing themselves to the danger of being possibly hit by the vehicle.